An improved process for the production of a saturated aliphatic monocarboxylic acid containing 6 to 9 carbon atoms by the oxidation of the corresponding aldehyde of the acid in the presence of a catalyst comprising copper and manganese is described in copending application, U.S. Ser. No. 345,890 filed Feb. 4, 1982, now abandoned, and assigned to Celanese Corporation. In another copending application, U.S. Ser. No. 423,899 filed Sept. 27, 1982, now U.S. Pat. No. 4,487,720, and assigned to Celanese Corporation, a further improvement is described in the production of a saturated aliphatic monocarboxylic acid containing 5 to 9 carbon atoms using a one stage oxidation of the corresponding aldehyde to the acid in the presence of a catalyst comprising copper and manganese compounds soluble in the saturated aliphatic monocarboxylic acid. In both of these processes, an anhydride of C.sub.5 -C.sub.9 saturated aliphatic monocarboxylic acid, in an amount from about 1 to about 20 weight percent or higher, of the total reaction product is produced. The anhydride, a by-product of the aldehyde oxidation, can be hydrolyzed completely to the acid in the presence of water at room temperature and atmospheric pressure over an extended period of time such as about 6 hours to about 20 hours or longer. However, the necessity of taking this much time to recover the acids from the anhydride by hydrolysis, or alternatively, the discarding of the anhydride resulting in the complete loss of the corresponding acid, is a serious economic detriment to commercial production of the acids by these processes.
There are various prior art processes for the production of anhydrides from aldehydes wherein hydrolysis of the anhydride is disclosed. However, the anhydrides are considered desirable products in the context of these processes and it is therefore desired to inhibit such anhydride hydrolysis. For example, in U.S. Pat. No. 2,293,104 entitled "Oxidation of Aldehyde" issued to Bludworth Aug. 18, 1942 and the glutaric anhydride process described in U.S. Pat. No. 2,820,821 entitled "Process for Oxidizing Glutaraldehydes" issued to Guest et al Jan. 21, 1958, the hydrolysis of these anhydrides in the presence of water, were found to be rapid at temperatures below 100.degree. C. and considered detrimental to the process. In the production of C.sub.5 -C.sub.9 saturated aliphatic monocarboxylic acid, the by-product anhydride is not desired because it is slow in its hydrolysis at temperatures below 100.degree. C. and rapid means of acid hydrolysis is required.